The following is a changelog for JavaScript from Netscape Navigator 4.0 to 4.5. The old Netscape documentation can be found on archive.org. Netscape Navigator 4.5 was released on October 19, 1998.

The most significant change in JavaScript 1.3 was compliance with ECMA-262 and Unicode by removing inconsistencies between JavaScript 1.2 and the new ECMA standard (which was published in June 1997). Additional features of version 1.2, at the time not specified by ECMA-262 were kept in the JavaScript language (see below for a list of differences).

JavaScript versions

Netscape Communicator and Navigator 4.06 and 4.5 executes JavaScript language versions up to 1.3. Note that Communicator and Navigator 4.0-4.05 and earlier ignored scripts with the language attribute set to "JavaScript1.3" and higher.

The length of an array (property length) is now an unsigned, 32-bit integer.

Array.prototype.push(): In JavaScript 1.2, the push method returned the last element added to an array. Under JavaScript 1.3, push returns the new length of the array.

Array.prototype.slice(): In JavaScript 1.2, the splice method returned the element removed, if only one element was removed (howMany parameter is 1). In JavaScript 1.3, splice always returns an array containing the removed elements. If one element is removed, an array of one element is returned.